(1) Field
This invention relates to a method for locating at least one touch on a touch-sensitive surface of an object. It also relates to a device for implementing this method.
(2) Description of the Related Art
There are many known objects that have a touch-sensitive surface, including mobile phones and other portable personal digital assistance devices. Their touch-sensitive interface is usually a flat rectangular screen with which a user can interact using a stylus or one or more fingers. Note, however, that the invention relates more generally to any type of object having a touch-sensitive surface that is not necessarily flat or rectangular in shape.
Each of these objects implements a method for locating at least one touch using one or more detection techniques.
The international patent application published under number WO 2006/133018 discloses a method for locating a touch on a touch-sensitive surface implementing multiple independent detection techniques, each providing an estimated location and comprising a step for cross-checking the estimates provided according to the various techniques in order to obtain a final result with improved accuracy. Among the considered techniques, one uses the repeated transmission in the touch-sensitive surface of elastic mechanical waves, such as surface acoustic waves, and the detection of these elastic mechanical waves to locate a touch by analyzing the interference of this touch on the detected waves. Because the implementation of this considered technique in this document does not provide a highly accurate estimate, it is advantageously combined with other techniques in order to refine the estimate. However, the multiplication of location techniques used slows down the processing of the sensed signals.
A method for locating using only one detection technique and analysis of detected signals is preferred. In particular, the invention more specifically relates to a method implementing only one technique for locating by analyzing the interference of a single or multiple touch on the propagation of elastic mechanical waves in a touch-sensitive surface, making it possible for it to provide an accurate estimate.
The invention therefore applies to a method for locating at least one touch on a touch-sensitive surface of an object that comprises the following steps:                monitoring of at least one touch by propagating, in the touch-sensitive surface of the object, elastic mechanical waves from at least one transmitting point of the object, and by detecting said elastic mechanical waves in at least one reception point of the object, in order to obtain at least one sensed signal, and        locating at least one touch on the touch-sensitive surface of the object by comparing certain characteristics of the sensed signal to a set of reference characteristics.        
Such a method is described in the international patent application published under the number WO 2008/142345. It provides for an accurate location by propagating waves having multiple frequency components corresponding to vibratory natural frequencies of the object. The propagation of these waves over a period of time in the touch-sensitive surface can identify patterns of vibration with different wavelengths, including resonance figures of bending modes. These have the characteristic of being more highly disrupted than resonance figures of modes of vibrations in the plane of the touch-sensitive surface of the object, so that the cushioning generated by a finger in contact with the surface, even if it is thick, varies significantly from one normal mode to another, and from one position of contact to another. It is then possible to locate a touch by a learning method, once a sufficient number of resonance figures are identified on the surface of the object.
However, many problems are not resolved by this method, such as recognizing, locating, and interpreting a multiple touch. Document WO 2008/142345 shows that the cushioning is not necessarily a linear function of the cover surface (except to choose a subspace of resonance modes), and when it is a linear function of the cover surface, it does not indicate whether it is always possible to locate a touch. Moreover, for cushioning to be a linear function of the contact surface, the energy must be evenly distributed on the surface of the object. In this case, however, there would no longer be any resonance, vibrational nodes, or vibrational antinodes. There would no longer be anything to distinguish the position of a touch.
There are other known methods for recognizing and/or interpreting multiple touches.
The international patent application published under number WO 2005/114369 describes, for example, a transparent touch-sensitive screen on which multiple touches are detected using a capacitive technology. This technology, however, has the drawback of requiring a transparent layer of electrodes and an array of capacitive sensor nodes.
The international patent application published under number WO 2008/085785 describes another example of a method for identifying and distinguishing the nature of a multiple contact (thumb, palm) by an analysis consisting of segmenting the obtained touch-sensitive image and identifying the discretized pattern using predefined models. This method has the drawback of requiring a discretized touch-sensitive interface.
The international patent application published under number WO 2008/085759 describes another example of a method for merging data from an interface with multiple touches. However, this method requires at least one secondary device and data synchronization from multiple devices.
Finally, the international patent application published under number WO 2008/085784 describes a touch-sensitive screen device that uses a dictionary of gestures that associates multiple touch to functions. However, the implemented method requires a comparison with all of the predefined elements in order to recognize a movement, and it only takes into account basic parameters of the multiple touches.
Another problem associated with the method described in document WO 2008/142345 resides in the high selectivity of the resonance figures and in the fact that it is then necessary to have a good frequency resolution in order to measure an amplitude at resonance peaks or at least to be able to carry out an interpolation to extrapolate the value of a resonance peak with or without contact. However, this method is highly accurate only with resonance figures. By working outside of the object's vibratory natural frequencies, it is possible to also obtain a stationary state of propagation in the touch-sensitive surface, but the obtained figures are much less discriminating.
Yet another problem associated with this method resides in the time to establish a stationary state of propagation in the touch-sensitive surface, as required to obtain the resonance figures. This time lengthens the processing time for locating a touch.
It may therefore be desirable to provide a method for locating at least one touch on a touch-sensitive surface of an object that overcomes at least some of the problems and constraints mentioned above.